Modal pop up boxes are becoming more and more common. Your screen goes dark then a sign up form appears or worse, an ad. They are usually triggered by either scrolling to a certain point on a page or after a time interval. Normally you can close the window or press escape and it goes away. Others are more aggressive and don't let you continue unless you sign up.
Link farming is the practice where you gather a bunch of websites and have them link to each other. On the surface it seems like a good idea. If I have a bunch of websites all linking to me then it will increase my search engine rankings. Right?
Wrong! Search engines are smart these days.